The point of this build is to make Renata Glasc deal some burst damage, and still provide utility for the team. Renata currently is one of 3 least popular league characters, with Rek'sai and Skarner. I belive it's like that because her release was rather silent and passed by unnoticed by the majority, but mostly because she is borderline unplayable. Her patch history is made out of nerfs and bug fixes. Her scaling was butcherd by indie devs, which led to her being build as a tank and provide utility with items she carries, her W and ult. Her E and Q are almost useless. Both too slow to hit reliably, both have to bad scaling. Base hp amd mana are terrible as well. All that led to tank Renata being the only way to play her.
I myself do not like to play her that way. She feels wrong when i build her the way its recommended. So i decided to experiment a little, and came up with this silly built for her. It is NOT made for some serious ranked playing, so please, do not try to built her that way in ranked, only if do not want to troll your teammates

I will start with runes.
In majority of cases people built resolve and domination. I dont like how resolve feels on her, so tried to go with aery, and i liked it way more. Comet is here for more damage focused build. The rest of the runes are focused on attempt of fixing her weak points. The domination gives a bit more damage and a deep ward, which is just a good rune for a support.
My choises are of course filled with mistakes and a lot could be improved, but all this is just for fun.

Rushing boots will give you more chances of hitting the Q and E, Scender will give mana regeneration and a bit of ap and an additional 20 damage on auto attack, after you use your E, Rabbadon's will give us some parody of a better scaling and a lot of ap, mandate will give some ap, mana regen and a very nice passive, that works good with Reanta's passive, since they both need teammates to proc it, and the Lich bane will give us more ap and some more damage on our first shot.

Idea of this build is to hit emeny with E, than land an AA, and just hide behind a teammate, before they proc all your marks and then so it all over again, occasionally landing Q for some CC. Renatas first attack deals additional damage due to passive, Lich bane will give even more damage, if we first hit any of our abilities, zac'zac will shred some more hp, commet will add some more, and Scender will gice additional 20 damage. The ult doesnt scale and cant be really improved by any means, exept, of course, the cooldown.

I hope this will gie some reason to play Renata, maybe then Riot will remember about her existence. Have a good day a game aswell.